1. Field of the Invention
The present invention is in the field of nondestructive testing by the penetrant inspection method and provides a dual purpose penetrant and dual purpose developer enabling the system to be used under either white light excitation or excitation by ultraviolet light.
2. Description of the Prior Art
There have been some disclosures of dual purpose penetrant systems for some time. Generally, the compositions employed in such systems are based either on a single fluorescent dye in combination with one or more cascading agents.
For example, when using the system described in U.S. Pat. No. 3,028,338, the developed indications are reasonably deep in visible color and compare favorably with standard visible dye indications. However, the fluorescent counterparts are essentially void of brilliance and the indications are not nearly as good as those obtained with conventional fluorescent systems on the market. It is believed that the reduced intensity fluorescent indications are due to a phenomenon known as fluorescent quenching which usually occurs when the concentration of the fluorescent material exceeds a predetermined value.
A different approach to dual purpose penetrant systems has been employed in U.S. Pat. No. 3,557,015. In this patent is described a system in which a non-fluorescent dye is combined with a fluorescent dye and used simultaneously in the penetrant to provide two different levels of sensitivity. The theory is that the visible non-fluorescent dyes are better able to detect large surface cracks while the fluorescent dyes are more useful in connection with the very fine surface cracks.